Quantum magnetic oscillations in crystals are typically understood in terms of Bohr-Sommerfeld quantisation, the frequency of oscillation is given by the area of a closed electron trajectory. However, since the 1970s, oscillations have been observed with frequencies that do not correspond to closed electron trajectories and this effect has remained not fully understood. Previous theory has focused on explaining the effect using various kinetic mechanisms, however, frequencies without a closed electron orbit have been observed in equilibrium and so a kinetic mechanism cannot be the entire story. In this work we develop a theory which explains these frequencies in equilibrium and can thus be used to understand measurements of both Shubnikov-de Haas and de Haas-van Alphen oscillations. We show, analytically, that these frequencies arise due to multi-electron correlations. We then extend our theory to explain a recent experiment on artificial crystals in GaAs two-dimensional electron gases, which revealed for the first time magnetic oscillations having frequencies that are half of those previously observed. We show that the half-frequencies arise in equilibrium from single-particle dynamics with account of impurities. Our analytic results are reinforced by exact numerics, which we also use clarify prior works on the kinetic regime.
Orbital diamagnetism requires closed orbits according to the Liftshiftz-Kosevich theory. Therefore, one might expect that open Fermi surfaces do not have a diamagnetic response. Contrary to this expectation, we show that open orbits in finite systems do contribute a magnetic response which oscillates between diamagnetism and paramagnetism. The oscillations are similar to the Aharonov-Bohm effect, because the oscillation phase is set by the number of flux quanta through the area defined by the width of the sample and the distance between adjacent atomic layers. The magnetic response originates …
In a Weyl orbit, the Fermi arc surface states on opposite surfaces of the topological semimetal are connected through the bulk Weyl or Dirac nodes. Having a real-space component, these orbits accumulate a sample-size-dependent phase. Following recent work on the three-dimensional Dirac semimetal cadmium arsenide (Cd3As2), we have sought evidence for this thickness-dependent effect in quantum oscillations and quantum Hall plateaus in (112)-oriented Cd3As2 thin films grown by molecular beam epitaxy. We compare quantum transport in films of varying thickness at apparently identical gate-tuned car…
Theoretical study of Magnetoresistance Oscillations in Semi-parabolic Plus Semi-inverse Squared Quantum Wells in the Presence of Intense Electromagnetic Waves
We consider observation of Aharonov-Bohm oscillations in clean systems based on the flow of topologically protected currents in silicene and bilayer graphene. The chiral channels in these materials are defined by the flips of the vertical electric field. The line of the flip confines chiral currents flowing along it in the direction determined by the valley. We present an electric field profile that forms a crossed ring to which four terminals can be attached, and find that the conductance matrix elements oscillate in the perpendicular magnetic field in spite of the absence of backscattering. …
Nonsmooth Bloch Oscillations in Non-Hermitian Systems
Advanced Institute for Materials Research (WPI-AIMR), Tohoku University（东北大学先进材料研究所）；RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), RIKEN（理化学中心交叉理论与数学科学中心）
We revisit the problem of diffusion in a driven system consisting of an inertial Brownian particle moving in a symmetric periodic potential and subjected to a symmetric time-periodic force. We reveal parameter domains in which diffusion is normal in the long time limit and exhibits intriguing giant damped quasiperiodic oscillations as a function of the external driving amplitude. As the mechanism behind this effect we identify the corresponding oscillations of difference in the number of locked and running trajectories which carries the leading contribution to the diffusion coefficient. Our fi…
